Desmin and CD34 positivity in cellular fibrous histiocytoma: an immunohistochemical analysis of 100 cases

BACKGROUND: Cellular benign fibrous histiocytoma (CBFH) represents a morphologic variant of cutaneous fibrous histiocytoma (FH). Because of its relative monomorphism and frequent fascicularity, CBFH can easily be mistaken for a malignancy. In fact, CD34, often used to distinguish CBFH from dermatofibrosarcoma protuberans (DFSP), can also be positive. To add to the confusion, desmin positivity may also be observed in a subset of CBFH. Desmin and CD34 expression often cause interpretative difficulty which may lead to misdiagnosis. Our aim was to examine the incidence of desmin and CD34 expression in CBFH. METHODS: One hundred consecutive cases of morphologically typical CBFH were retrieved from consultation files. Clinicopathologic and immunohistochemical features were evaluated. RESULTS: SMA positivity was found in tumor cells in 93 of 100 cases (93%). Desmin positivity was found in 32 of 100 cases (32%). CD34 was positive in 6 of 100 cases (6%). There was no evident correlation between immunophenotype and anatomic site or other clinical variables. CONCLUSION: Frequent desmin (32%) and occasional CD34 (6%) expression are encountered in CBFH. Desmin positivity can be explained on the basis of myofibroblastic differentiation. The occasional CD34 positivity in a subset of CBFH should not be a deterrent from making the correct pathologic diagnosis, based on characteristic morphologic features.